just keep riding
Join Date: Feb 2005
Location: Milledgeville, Georgia
Posts: 13,560
Bikes: 2018 Black Mountain Cycles MCD,2017 Advocate Cycles Seldom Seen Drop Bar, 2017 Niner Jet 9 Alloy, 2015 Zukas custom road, 2003 KHS Milano Tandem, 1986 Nishiki Cadence rigid MTB, 1980ish Fuji S-12S
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For whatever reason, when road disc brakes started happening, rather than use the 15mm standard of most MTB front hubs, they decided to make a new 12mm standard. At first, gravel bikes tended to go with the 15mm, but now they are adopting the 12mm road standard. This is leaving a lot of prfectly good older MTB wheels stranded. As wider rims became popular with MTBs, the 19-22mm inner width rims that had been popular for years became out of favor for 2"+ MTB tires, but were perfect for 35-45mm gravel tires.
If you have a gravel bike for with 15mm TA, you can find those wheels fairly cheap. But if you have a 12mm TA, you can only use them if you are lucky enough to have end caps that have 19mm outer diameter instead of the 21mm OD that most 15mm TA hubs use. I had mixed luck when I changed from the All City Cosmic Stallion which used 15mm TA to the Black Mtn MCD which uses 12mm TA. I was lucky that the Roval carbon wheels that I picked up for a steal on closeout had 19mm OD end caps, so I was able to put a 12mm sleeve inside the 15mm hub and use the wheel. No such luck with the SP dynamo hub on the 650B wheels I built. That hub has 21mm OD ends which are not removable and do not fit in the hooded dropout of the MCD's fork.